Continuous freezing machines are used to extrude hard ice in a symmetric column that is easily cut, packed, stored and transported. Continuous freezing machines are described generally in U.S. Pat. No. 2,571,506 (Watt I) and U.S. Pat. No. 2,639,594 (Watt II) as well as U.S. Pat. No. 2,071,465 (Huber), U.S. Pat. No. 2,374,997 (Hill), U.S. Pat. No. 2,471,655 (Rundell) and U.S. Pat. No. 2,542,891 (Bayston), all of which are incorporated herein by reference.
FIG. 1 shows a known continuous freezing machine 10. In general, a freezing cell 12, shown as a vertically tapered, externally refrigerated open ended frusto-conical cylinder, is mounted within a reservoir 14 of cooled water 16. The major end 18 of freezing cell 12 is above reservoir 14 with minor end 20 of freezing cell 12 submerged below the water line 22 of reservoir 14. A stub cylinder 24 connects to minor end 20. A motor 26 forces a ram 28 and plunger 30 to vertically reciprocate within stub cylinder 24.
Operation of freezing machine 10 begins by placing ram 28 and plunger 30 in their "at-rest" position at the bottom of stub cylinder 24. Water is introduced to freezing cell 12 by pump 32. Refrigerated inner wall 34 of freezing cell 12 chills the water until a solid ice core 36 begins to form at minor end 20. The formation of ice core 36 chills unrefrigerated inner wall 38 of stub cylinder 24 leading to the formation of an ice sleeve 40 on inner wall 38.
When ice sleeve 40 reaches a predetermined thickness (typically 3/8" or 1/2"), motor 26 is activated to drive ram 28. As a result, plunger 30 scrapes inner wall 38 and breaks up ice sleeve 40 as it moves upward in stub cylinder 24, eventually compacting the resulting ice chips against ice core 36.
Referring to FIG. 2, ram 28 continues its upward movement and breaks ice core 36 away from inner wall 34 in one piece and lifts ice core 36 slightly (approximately 0.10") creating a thin annular crevice 42 between ice core 36 and inner wall 34. Water from pool 44 above ice core 36 is drawn into and fills annular crevice 42. Ram 38 maintains its position at the top of its stroke allowing the water occupying annular crevice 42 to freeze to inner wall 34 and ice core 36. When this occurs, ram 28 and plunger 30 are no longer needed to support ice core 36 in its current position.
Ram 28 and plunger 30 then return to their "at-rest" position at the bottom of stub cylinder 24 and pause to allow the complete freezing of the water in annular crevice 42 and for a new ice sleeve 40 to form on inner wall 38. Typically, this rest lasts for approximately ten seconds. The ram action then commences again with the upward stroke of ram 28 and plunger 30.
In this fashion, continuous freezing machine 10 forms a column of hard ice conforming to the shape of inner wall 34 at major end 18. This column of hard ice may be cut into blocks that are easily stacked, stored and transported as ice core 36 advances upward past major end 18.
However, continuous freezing machines similar to that in FIGS. 1 and 2 only work efficiently in short bursts. Operation of continuous freezing machine 10 for more than a few hours at a time leads to a degradation of the symmetry of ice core 36, and eventually to the splitting of ice core 36 into a plurality of irregular prisms. Irregular prisms of ice are unmarketable as they lack the uniformity needed for efficient storing, stacking and transportation. Once irregular ice prisms form, continuous freezing machine 10 must be stopped, the ice prisms within freezing cell 12 removed, and the freezing process initiated again. This constant restarting every few hours reduces the amount of marketable ice a continuous freezing machine 10 can produce.
It would be beneficial for freezing machines to produce a uniform ice core continuously without the need for restarting due to the ice core shearing into irregular prisms without significantly increasing the cost of the freezing machine or its operation.